Engine efficiency can be increased while providing a desired engine output capacity by lowering engine displacement and compressing air supplied to the engine. Lowering the engine displacement can reduce engine pumping losses and pressurizing engine intake air can increase output power of a smaller displacement engine. Consequently, a smaller displacement engine can provide improved fuel economy as compared to a larger displacement engine while providing an amount of power that is similar to the larger displacement engine. However, compressors can experience surge when flow through the compressor is low and when the pressure differential across the compressor is relatively high. Surge may be undesirable for several reasons including because surge may induce undesirable noise from the engine air intake system.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for supplying air to an engine, comprising: controlling air flow to a compressor via a first throttle; controlling air flow from the compressor to engine cylinders via a second throttle; and at least partially closing the first throttle during a condition of surge of the compressor.
By closing a throttle upstream of a compressor during conditions of compressor surge it may be possible to reduce the amount of noise that is noticeable to a vehicle operator. For example, if a compressor bypass valve is opened to reduce surge, the sound of air bypassing the compressor and returning to the compressor inlet may be less noticeable when a throttle located upstream of the bypass valve and compressor in a direction of air flow into the engine is at least partially closed. Closing the throttle can impede propagation of should waves from the bypass valve to the air inlet air box so as to reduce the amount of sound emanating from the air inlet air box. As a result, the amount of compressor surge induced noise may be reduced. In addition, boost pressure can be conserved by closing an air inlet throttle during surge conditions. Thus, instead of releasing compressed air to the atmosphere via the air box, the compressed air may be held within the engine air intake system where it can be consumed by the engine.
The present description may provide several advantages. Specifically, the approach may reduce engine noise by limiting noise emanating from the air inlet air box. Further, the approach can conserve pressurized air for engine use rather than releasing the compressed air to atmosphere. Consequently, the approach may reduce the amount of work used to pressurize engine air. As a result, the approach may improve fuel economy since the work put into compressing air may be recovered.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.